The stunt is the work of global activist group Avaaz, which wants Zuckerberg, Internet CEOs and government regulators to fight disinformation campaigns across Facebook and other social platforms.

“We know Facebook is doing things to address the fake news problem, but they are doing it in a way to that is too small and too secretive,” Avaaz campaign director Nell Greenberg told CNN.

“We want Facebook to tell the truth regarding the work that is being done to stop this and the scale of the fake news and fake post problem. We just want to know the transparency of the problem and what is being done to tackle it,” Greenberg said.

This is the first time Zuckerberg will personally sit for questions from Congress. His testimony marks a pivotal moment for Facebook, as Zuckerberg will spend two days answering lawmakers’ questions about what the company is doing to protect users’ privacy.